Phosphor rare earth oxychloride compositions

ABSTRACT

A CLASS OF COMPOUNDS IS FOUND PARTICULARLY EFFECTIVE FOR UP-CONVERSION OF INFRARED RADIATION TO LIGHT OF VISIBLE WAVELENGTHS. THESE COMPOUNDS, EXEMPLIFIED BY THE OXYCHLORIDES AND FLUOROCHLORIDES, CONTAIN THE ION PAIR YB3+-ER3+, YB3+--HO3+, YB3+-TM3+ OR MIXTURES THEREOF.

2, 1974 w. H. GRODKIEWICZ ETTAL 3,822,215

PHOSPHOR RARE EARTH OXYCHLQRIDE COMPOSITIONS Original Filed April 16,1969 lifetime United States Patent Office Patented July 2, 19743,822,215 PHOSPHOR RARE EARTH OXYCHLORIDE COMPOSITIONS -William HenryGrodkiewicz, Murray Hill, Shobha Singh,

Summit, and Le Grand Gerard Van Uitert, Morris Township, County ofMorris, N.J., assignors to Bell Telephone Laboratories, Incorporated,Murray Hill,

Original application Apr. 16, 1969, Ser. No. 822,847, now Patent No.3,659,136. Divided and this application Jan. 24, 1972, Ser. No. 220,143

Int. Cl. C09k 1/08 US. Cl. 252-301.4 H 1 Claim ABSTRACT OF THEDISCLOSURE A class of compounds is found particularly effective forup-conversion of infrared radiation to light of visible wavelengths.These compounds, exemplified by the oxychlorides and fluorochlorides,contain the ion pair Yb +-Er Yb -Ho Yb'+--Tm or mixtures thereof.

CROSS REFERENCE TO RELATED APPLICATION This application is a division ofmy copending application, Ser. No. 822,847, filed Apr. 16, 1969, nowPat. No. 3,659,136.

BACKGROUND OF THE INVENTION 1. Field of the invention There is arecognized need for a low power level, long electro-luminescent device.While several avenues have been investigated, many consider the directemitting P-N junction semiconductor diode to be the most promising.

There is a large body of reported work considering gallium phosphidediodes. Depending on the dopant used, GaP junctions may emit in the redor the green. The red emitting device is more efficient and itsdevelopment has now attained a fair level of sophistication. Recently,such .a diode operating at an efiiciency of 3.4 percent was reported; I.Ladany, Electro-Chemical Society Meeting, Montreal, Oct. 11, 1968, Paper610, RNP.

Silicon-doped GaAs diodes are several times as efficient (up to about 20percent at room temperature) but emit at infrared rather than visiblewavelengths. The possibility exists that the GaAs infrared output may beup-converted to a visible wavelength with reasonable conversionefiiciency.

It was recently announced that appreciable output at a visiblewavelength had been obtained by use of a conversion phosphor coating onsuch a silicon-doped GaAs diode, see S. V. Galginaitis et al.,International Conference on GaAs, Dallas, Oct. 17, 1968, SpontaneousEmission Paper No. 2. The coating, which depends on a twophoton process,utilizes the ytterbium-erbiurn ion pair in a host of lanthanum fluoride.

In the coated device, infrared emission with a peak wavelength at about0.9312 (micron) is absorbed by Yb with a peak absorption at 0,98,12.Transfer and twophoton excitation results in Er green emission at 054p.

SUMMARY OF THE INVENTION GaAs infrared diodes provided with a conversioncoating of a compound having at least one each of two different anionsor at least one anion vacancy in some unit cells (or formulaequivalent-amorphous matrices) and also containing the Yb +Er Yb +Ho Yb+-Tm ion pair or mixtures thereof showing increased visible output ascompared with LaF coated devices. Improved conversion efficiencyis.attributed, at least in part, to the anisotropic nature of the hostenvironment due to a nonsymmetrical array of anions or differences inneighboring anions with its attendant crystal field splitting for the Ybabsorption spectra.

In the exemplary oxychloride and fluorochloride hosts, relatively broadYb absorption peaks at about 0.94 1. permitting a particularly goodmatch for existing silicondoped GaAs diode emissions and such hostmaterials constitute a preferred embodiment of this invention.

Depending on the structure and the concentration of sensitizer (Yb andactivator (Er ions in such hosts, blue, green or red fluorescence can berealized. Strong excitation may result in appreciable green and blueemission at wavelengths of about 0.55 and 0.41 respectively, and strongemission in the red at a wavelength of about 0.66 1. However, forexample, in the YOCl and Y OCl hosts, fluorescence appears red or green,respectively, to the eye for the lowest levels of discernible emission.Improvement in attainable brightness in the green in such cases and/oran adjustment in the apparent output color may result from the additionof limited quantities of holmium (Ho which typically emits at about 0.542 in the green.

Attention to the considerations set forth above sometimes dictatespreferred ranges of activator (Er Ho or Tm) and sensitizer (Yb ioncontents. Together these may be less than the total cation content asvarious inactive cations such as yttrium, lanthanum, lutecium orgadolinium may be utilized.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a front elevational view ofan infrared emitting diode having a phosphor converting coating in accordance with the invention; and

FIG. 2 is an energy level diagram in ordinate units of wave numbers forthe ions Yb Er, Ho and Tm within the crystallographic environmentprovided by a composition herein.

DETAILED DESCRIPTION 1. The Drawing Gallium arsenide diode 1 containingP-N junction 2, defined by P and N regions 3 and 4, respectively, isforward biased by planar anode 5 and ring cathode 6 connected to powersupply not shown. Infrared radiation is produced by junction 2 underforward-biased conditions, and some of this radiation, represented byarrows 7, passes into and through layer 8 of a phosphorescent materialin accordance with the invention. Under these conditions, some part ofradiation 7 is absorbed within layer 8, and a major portion of thatabsorbed participates in a two-photon or higher order photon process toproduce radiation at a visible wavelength/s. The portion of thisreradiation which escapes is represented by arrows 9.

The main advantage of the defined phosphors is best described in termsof the energy level diagram of FIG. 2. While this energy level diagramis a valuable aid in the description of the invention, two reservationsmust be made. The specific level values, while reasonably illustrativeof those for the various included compositions of the noted type, aremost closely representative of the oxychloride systems either of theYOCl or Y OCl stoichiometries. Also, while the detailed energy leveldescription was determined on the basis of carefully conductedabsorption and emission studies, some of the information contained inthe figure represents only one tentative conclusion. In particular, theexcitation routes for the 3 and 4 photon processes are not certainalthough it is clear that certain of the observed emission represents amultiple photon process in excess of doubling. The diagram is sufficientfor its purpose; that is, it does describe the common advantages of theincluded host materials and, more generally, of the included phosphorsin the terminology which is in use by quantum physicists.

For example, phosphor coating 8 may contain an additional inertingredient or ingredients serving, for example, to improve adhesion tothe substrate 4 and/or to reduce light scattering between particleswhere coating 8 is particulate. Still another purpose which may beserved by an inert ingredient is to encapsulate the coating material soas to protect it from any harmful environment.

FIG. 2 contains information on Yb Er Ho and Tm. While the pairs Yb +-Hand Yb +-Ti:t1 are not the most efiicient for energy up-conversion, theformer does provide a strong green fluorescene and enable a desirablecolor shift and improvement in efficiency when included as an ancillarypair with Yb +-Er Further, the Yb +-Tm couple provides a source of bluefluorescence.

The ordinate units are in wavelengths per centimeter (cm- These unitsmay be converted to wavelength in angstrom units (A.) or microns (a) inaccordance with the relationship:

10 Wave numbers Wave numbers Wavelength-- The left-hand portion of thediagram is concerned with the relevant manifolds of Y-b in a host of theinvention. Absorption in Yb results in an energy increase from theground manifold Yb F- to the Yb F manifold. This absorption defines aband which includes levels at 10,200 cmr 10,500 cmr' and 10,700 cm.- Thepositions of these levels are aifected by the crystal field splittingwithin the structures having at least one each of two different anionsor at least one anion vacancy per unit cell or formula unit. In theOxychlorides, for example, they include a broad absorption which peaksat about 094 (10,600 cmr there is an eflicient transfer of energy from asilicon-doped GaAs diode (with its emission peak at about 0.93 0. Thiscontrasts with the comparatively small splitting in lanthanum fluorideand other less anisotropic hosts in which absorption peaking is about0.98; for Yb The remainder of FIG. 2 is discussed in conjunction withthe postulated excitation mechanism. All energy level values and allrelaxations indicated on the figure have been experimentally verified.

2. =Postulated Excitation Mechanisms Following absorption by Yb ofemission from the GaAs diode, a quantum is yielded to the emitting ionEr (or as also discussed in conjunction with the figure, to H0 or Tm Thefirst transition is denoted 11. Excitation of -Er to the 1 is almostexactly matched in energy (denoted by m) to the relaxation transition ofYb. However, a similar transfer, resulting in excitation of Ho to H0 1or Tm to Tm H requires a simultaneous release of one or more phonons(+P). The manifold Er I has a substantial lifetime, and transfer of asecond quantum from Yb promotes transition 12 to the 'Er F manifold.Transfer of a second quantum to H0 or Tm results in excitation to H0 8or, after internal relaxation from Tm H to Tm H (by yielding energy asphonons in the matrix), excitation to Tm F with simultaneous generationof a phonon. Internal relaxation is represented on this figure by thewavy arrow f In erbium, the second photon level (Er F has a lifetimewhich is very short due to the presence of close, lower lying levelswhich results in rapid degradation to the Er S state through thegeneration of phonons.

The first significant emission of Er is from the Er S state (18,200 cm.-or 0.55 in the green). This emission is denoted in the figure by thebroad (double line) arrow A. The reverse of the second photonexcitation, the nonradiative transfer of a quantum from Er F back to Ybmust compete with the rapid phonon relaxation to Er S and is notlimiting. The phonon relaxation to Er F also competes with emission Aand contributes to emission from that level. The extent to which thisfurther relaxation is significant is composition dependent. The overallconsideration as to the relationship between the predominant emissionsand composition are discussed under the heading Composition.

Green emission A at a wavelength of about 0.5 5 corresponds to thatwhich has been observed for Er in LaF In accordance with this invention,it has been shown that the structures having mixed anions or anionvacancies with large resulting anisotropic environments about thecations are characterized by large crystal field splittings whichsignificantly improve the absorption of GaAszSi emission by Yb Largecrystal field splittings also result in increased opportunity forinternal relaxation mechanisms involving phonon generation which thusfar have not been found to be pronounced in comparable but moreisotropic media. For Er this enhances emission B at red wavelengths.Erbium emission B is, in part, brought about by transfer of a thirdquantum from Yb to Er which excites the ion from Er S to El' Gq/g withsimultaneous generation of a phonon (transition 13). This is followed byinternal relaxation to Er G which, in turn, permits relaxation to Er Fby transfer of a quantum back to Yb with the simultaneous generation ofa phonon (transition 13'). The Er Fg/z level is thereby populated by atleast two distinct mechanisms and indeed experimental confirmationarises from the finding that emission B is dependent on a power of theinput intensity which is intermediate in character to thatcharacteristic of a three-phonon process and that characteristic of atwo-phonon process for the Y OCl, host. Emission B, in the red, is about15,250 cmr or 0.66

While emissions in the green and red are predominant, there are manyother emission wavelengths of which the next strongest designated C isin the blue (24,400 cm.- or 0.41 This third emission designated Coriginates from the El' Hg g level which is, in turn, populated by twomechanisms. In the first of these, energy is received by a phononprocess from Er G The other mechanism is a four-phonon process inaccordance with which a fourth quanta is transferred from Yb to Erexciting from Er G (transition 14). This step is followed by internalrelaxation to Er D from which level energy can be transferred back to Ybrelaxing Er to Er H (transition 14').

Significant emission from holmium occurs only by a two-photon process.Emission is predominantly from H0 8 in the green (18,350 cm." or0.54;.t). A similar process in thulium also results in emission by athreephoton process (from Tm'G in the blue at about 21,000 cm. or 0.47The responsible mechanisms are clear from FIG. 2 and the foregoingdiscussion.

3. Material Preparation Since the phosphors of the invention are inpowder or polycrystalline form, growth presents no particular problem.Oxychlorides, for example, may be prepared by dissolving the oxides(rare earth and yttrium oxides) in hydrochloric acid, evaporating toform the hydrated chlorides, dehydrating, usually near 100 C. undervacuum, and treating with C1 gas at an elevated temperature (about 900C). The resulting product can be the one or more oxychlorides, thetrichloride or mixtures of these depending on the dehydratingconditions, vacuum integrity and cooling conditions. The trichloridemelts at the elevated temperature and may act as a flux to crystallizethe oxychlorides. The YOCl structure is favored by high Y contents,intermediate dehydration rates and slow cooling rates while more complexchlorides such as (Y, Yb) OCl are favored by high rare earth content,slow dehydration and fast cooling. The trichloride may subsequently beremoved by washing with water. Dehydration should be sufliciently slow(usually 5 minutes or more) to avoid excessive loss of chlorine.

Oxybromides and oxyiodides may be prepared by similar means usinghydrobromic acid and gaseous HBr or hydroiodic acid and gaseous HI inplace of hydrochloric acid and C1 in the process.

Mixed halides such as those containing both alkali metals and rareearths can be prepared by dissolving the oxides in HCl, precipitatingwith HF, dehydrating and melting the resulting material together near1000 C. in vacuum or simply by fusing an intimate mixture of the alkalimetal and rare earth halides in vacuum.

Lead or alkaline earth fluorochloride or the corresponding fluorobromidemay be prepared simply by melting the appropriate halides together invacuum. The products can, in turn, be melted together with the oxyhalideand/ or fluorohalide phosphors to adjust their properties.

Appropriate rare earth oxides have anion defect structures whichcontribute to the nonisotropic nature of the crystal field. Thesematerials can be prepared by heating their chlorides to form powders andby Flame Fusion to form crysals, if desired.

4. Composition The essence of the invention is the use of a host matrixfor the activator and sensitizer ions having at least one each of twodifferent anions or at least one anion vacancy in at least one percentof the unit cells or formula units. Examples of overall host compositonsare rare earth oxides and yttrium oxide where only six of eightavailable neighboring sites are occupied; rare earth and yttriumoxychloride, oxybromides, oxyiodides; the corresponding bismuthcompounds (those containing BiOCl, for example); the oxychalkogenides(those containing ThOS, for example); alkali metal rare earth (oryttrium) fluorohalides of the forms M +M '!'X M +M +X or M +M +X andalkaline earth or lead fiuorohalides of the form M +X where M +=Li, Na,K, Rb, Cs or Ti; M =Ca, Sr, Ba or Pb; M +=La, Gd, Lu, Y, Bi or Yb andX=F, Cl, Br or I. The one percent minimum requirement implies thepossibility of mixed host compositions and such mixtures may include anynumber of the foregoing.

The oxychlorides, oxybromides and oxyiodides are preferred embodimentsof the structures involved and, of these the oxychlorides are thepreferred class. The latter consist of at least two varieties althoughothers are not to be construed as excluded. These have variousstructures including (a) the tetragonal 7 4 D -P nmm structure in commonwith YOCl or (b) a hexagonal structure, with an oxygen to chlorine ratioof less than one, for which a composition with the analyzed metalratios: Y=56%, YB=43% and EF1%, lattice constants a =5.607 and 65:9.260and prominent d-spacings of 9.20, 2.33, 3.09, 4.62, and 2.83 are typicalAnalyses indicate a structure (RE) OCl where RE=Rare Earths Y,

for the latter. of these two structures, (b) is preferred due to agreater range of fluorescent characteristics and is generalized asY3OC17 for simplification herein.

While the structural considerations are paramount, the compositions mustalso contain the requisite ion pair Yb +-Er Yb +-Ho mixtures thereof, orYb +-Tm As described in conjunction with FIG. 2, initial transfer ofenergy is to Yb. A minimum of this ion is set at 5% based on totalcation content, since appreciably below this level transfer isinsufiicient to produce an expedient output efficiency regardless of theerbium content. A preferred minimum of about 10% on the same basis may,under appropriate conditions, result in an output intensity competitivewith the best gallium phosphide diode. The maximum ytterbium content isessentially 100% on the same basis, and it is an advantage ofcompositions of the invention that such rare earth levels may betolerated. For ytterbium content above however, brightness does notincrease substantially with increasing ytterbium; and this level,therefore, represents a preferred maximum. It has been noted that thestrong fluorescence of El may vary from essentially pure green emissionat about 0.55u to a mixture of green and red, the latter at about 0.66;.Due to the effect of exchange coupling of Yb to Er on internalrelaxation, red emission from erbium becomes dominant for largerytterbium concentration. Generally, ytterbium concentration betweenabout 20% and 50% results in mixed green and red output while amounts inexcess of about 50%, under most circumstances, result in outputapproaching pure red. A preferred range for a red emitting phosphorcoating, therefore, lies between 50% and 80% Yb The erbium range is fromabout 4 to about 20%. Below the minimum, erbium output is notappreciable. Above the maximum, which is only approached for high Ybconcentrations, internal radiationless processes substantially quencherbium output. A preferred range is from about A to about 2%. Theminimum is dictated by the subjective criterion that only at this leveldoes a coated diode with sufficient brightness for observation in anormally lighted room result. The upper limit results from theobservation that further increase does not substantially increaseoutput.

Holmium, recommended as an adjunct to erbium in conjunction withytterbium, as well as with ytterbium alone, may be included in an amountfrom about to about 5% to obtain green emission or to aid the greenoutput of erbium. Such activation may be desirable in the intermediate20% to 50% Yb range alone or when erbium is present as well as atgreater concentrations of the Yb. Lesser amounts of holmium producelittle discernible output as viewed by the eye. Amounts substantiallylarger than 2% result in no substantial increase and above about 10%result in substantial quenching. Thulium may also activate theoxychlorides, and its value is premised on its blue output. Amounts offrom about to about 5% are effective. Limits are derived from the sameconsiderations discussed with holmium.

Where the required cation content of the host is not met by the totalYb+Er+Ho+Tm, inert cations may be included to make up the deficiency.Such cations desirably have no absorption levels below and within asmall number of phonons of any of the levels relevant to the describedmultiphoton processes. A cation which has been found suitable isyttrium. Others are Pb, Gd, Na as well as other such ions listed above.

Other requirements are common to phosphor materials in general. Variousimpurities which may produce un wanted absorption or which may otherwisepoison" the inventive systems are to be avoided. As a general premise,maintaining the compositions at a purity level resulting from use ofstarting ingredients which are three nines pure (99.9%) is adequate.Further improvement, however, results from further increase in purity atleast to the five nines level.

Generally, preferred compositions herein contain two or more differentanions in at least 1% of the unit cells or equivalent. The anisotropiccrystal field conditions resulting from different anion site occupanciesin the same unit cell tend to increase overall quantum efficiency.However, it is noted that as little as 1% of such cells providessignificant improvement of properties. With reference to such unitcells, preferred compositions herein invariably contain either oxygen orfluorine at admixture with a different anion (this grouping is intendedto include oxychlorides). While the advantages gained by the use of theinventive materials are largely premised on increased brightness forequivalent conditions such as doping levels, it has also been noted thatvisible emission may be at a variety of or combination of wavelengths. nthe basis of a large number of experimental runs, some of which arerepresented below, it has been observed that red Er emission is enhancedby the presence of oxygen. In fact, as noted, for the simple oxychloridewith a 1:1 anion ratio, only red emission is apparent to the eye undermost conditions.

It has also been observed that the presence of chlorine results in asignificant improvement in overall brightness, again, for equivalentdoping and pump levels. This effect is essentially independent of theprevalent color of the visible output. Accordingly, a simple oxychlorideis brighter in the red than is a simple oxybromide which is also red. Afiuorochloride which emits largely in the green is brighter than is theequivalent fiuorobromide.

The two paragraphs above are concerned only with the unit cellscontaining mixed anions. While the minimal requirement for compositionsherein is about 1% of the total number of unit cells in the compositionbeing of such nature, further enhancement results as the number of cellsis increased. Under usual conditions, maximum overall efiiciency is, infact, obtained when all of the unit cells contain such mixed anions,although it is possible that circumstances may exist in which activatordoping levels are such as to result in concentration quenching.

5. Examples The following specific examples were selected from a largernumber to represent the more significant compositional variations. Whilethe preparatory procedure is described in detail in the first twoexamples, such description in each succeeding example is consideredunnecessarily repetitious. It is believed that the general preparatorytechnique described above is sufficient to enable a worker in the fieldto reproduce any composition within the inventive range.

Example 1 A composition represented nominally as o'i) o.29 o.u1)a 'z wasprepared from the following starting ingredients Grams Y O 1.58 Yb O1.14 Er O 0.038

All materials were particulate to facilitate dissolution. The oxidicmaterials were next dissolved in hydrochloric acid and this solvent wasnext evaporated to leave the mixed rare earth hydrated chloride. Theresidue 'was dried in air to remove unbonded (excess) H O. The resultingmaterial was next placed in a quartz tube which was connected to avacuum station after which tube and contents were maintained at 100 C.under vacuum for a period of four hours to remove water of hydration.With tube and contents still connected to the vacuum station,temperature was raised to 1000 C. to produce a molten mixture of rareearth trichloride and rare earth oxychloride. The contents were nextcooled and the trichloride was removed by dissolving in water. Crystalsof the approximate composition set forth were produced by spontaneousnucleation during cooling.

Crystals of the final composition were admixed with collodion and thecomposite was painted on the surface of a silicon-doped gallium arsenidediode capable of emitting at an infrared wavelength at about 0.93 2 whenforward biased. The diode was biased at about 1 volt in the forwarddirection under which conditions current flow was observed to be about 1ampere. The coated portion of the diode glowed an apparent yellow-redcolor (spectroscopically observed to represent a measure of green andred wavelengths). Quantum efiiciency (visible output divided by infraredabsorbed by the phosphor) was estimated to be at a level in excess of20%. Note: Maximum quantum efiiciency for the prevalent third-photontransition is 33 /3 since three quanta of infrared are by definitionrequired to produce one quantum of visible output.

Example 2 The approximate composition Li(Y -;Yb Er (F,Cl) was producedfrom the following starting ingredients:

The particulate starting materials were dissolved in hydrochloric acid.Hydrochloric acid was added resulting in the precipitation of whitepowder. The solvent was next removed by evaporating at 50 C. The powderwas again placed in a quartz tube and contents were dried under vacuumat C. for 4 hours to remove water of hydration. The temperature wasagain raised to 1000 C. to melt the product. Tube and contents werepermitted to cool so as to result in a particulate end product of thescheelite structure.

The powder was again mixed with collodion to minimize scatter loss andthe mixture was painted on a gallium arsenide diode as in Example 1.Under one-volt forward bias (as in Example 1), emission was green and ofan efficiency comparable to Example 1.

Example 3 The composition represented by the approximate formula Na(Y YbEr )F 01 was prepared by melting together at about 1300 C. an intimatemixture of:

Grams NaCl 0.058

NaF 0.378 YF 1.022 YbF 0.666 ErF 0.022

The final product had the Na ThF structure. This product too was mixedwith collodion and was painted on a GaAs diode which was biased as inExample 1. Color and apparent brightness were as in Example 2.

ADDITIONAL EXAMPLES 9 TABLE YbmggEro ocl R d- 0.99 '0.o1)3 7 Do. Yb0995H 0 o OC1 Gr eno.995 o.005)3 7 DO. Yb Tm OCl Blue- 0.995 0.005)3 7D0- 0.5 o,4 o.0 1 Red. Yb0 5Y( 49H00 010Cl Gl eln- Yb Y Tm OCl Blueo.50.49 '0.01) 3 7 R o.5 o.49 o.01)3 7 -r Green. 0.5 o.49 o.o1)3 -zBlueo.15 o.a4 'o.o1 o.15 0.a4 o.o1)3 'r t).29 o.7 o.o1 3 '7 o.29 o.ro.o1 0.oo5)3 7 o.29 o.q 'o.o1) s.9 o.1 Greeno.29 0.7 o.o1) s.9 o.1 0.29o.'r 0.o1) 3.9 o.1 Rb t).29 o.'z 'o.o1) 3.9 o.1 o.29 o.7 'o.o1) 3.9 o.1o 29 0,7 'u 01) z z o 29 o,'r 0 o1) z lz 0.29 o.'1 0.o1) 2 2 Rb u 29Y037 0131 z z D0- o,29 0.-7 o,01) z z o.29 0.1 o.o1) s.s o.o1

o 29 0.7 'o,01) o.29 o.'1 u.o1) a.9 o.1

o,z9 u q o.o1) K( o.29 o.'1 0.o1) 3 3 0.1

0.29 0,7 0 01) CS o.29 o.'1 0.u1) s .9C10J.

o,29 o.q 0.o1) 0C1 o.29 o.7 0.o1) 2 2' o.29 o.'r 'o.o1) o.29 n.'r 'o.o1)2 2 oze oxz 'nofl 0.29 o.'1 o.01) 2 2 n.29 o.'z '0.o1) D Rb o.29 o.'1'n.01) 2 z' 0.29 o.7 o.o1) 1 D0. o.29 o.'1 0.o1) z z' o.2e o.'1 o.or)(YboagYopqEro o DO- (Yb 29Y0 7E1'0 01) DO- I'FCl' (Ybo gYgflEl'gpJOClDO- BaFCl' (Ybo 29Y 7EI'o 0 D0- Na (Y o,29 'rE '0 1)F9 o,1 na o.29 o.'zo.o1) s.9 o.o1 s( o.29 0.'z 'o.o1) 5.9 0.o1 s o.29 0.7 'o.o1) 5.9 o.o1o.29 o.7 o.o1) 2 2' o.29 0.'z 'o.o1) 1 D0- (YbmggYof/EI' 01)F c1 o.aao.q 'o,o1) cl D0. PbFCl CS o.29 n.'1 'o.o1) 2 2 oes ori 'om) 1 D0. o.29o.'r 'o.o1) 2 z' oes oxr om) 0 1 Do.

' Na (Ybo ggYo Ero .01) FzClz 029 0.'i 'o.o1) Do. BaFCl o.2s o.'r 'o.o1)2 2 l 0 TABLE-Continued The invention has been described in terms ofessential ingredients. Accordingly, in the usual form of the invention,the exact form of the phosphor is not specified. Where this phosphor isincluded as an adherent coating on a diode, it may be desirable toinclude some inert material (inert from the phosphorescent standpoint).Such material may serve to improve adhesion between the phosphor and thediode and/or may serve the function of reducing light scattering betweenparticles in a coating or between the diode and the particles.

For the latter use, it is, of course, desired that the inert materialhave a refractive index which is approaching or exceeding that of thephosphor. In some cases, an inert material with an index approximatingthat of the GaAs is preferred. Typical index approximating that of theGaAs is preferred. Typical index values for this purpose areapproximately 2 to 3.5 on the usual scale in which vacuum is graded asunity. The use of such additional material or materials is of particularsignificance in the preferred embodiments in which the phosphor materialis made up of crystalline matter. Where the phosphor is itselfamorphous, the inert material may be of little advantage. In any event,where such additional material is incorporated in a phosphor coating,the amount is desirably kept to a minimum sufiicient for the intendedpurpose, be it to enhance adhesion and/or to reduce scattering. Sincethis additional material is inert from the phosphorescent standpoint, itotherwise acts only as a diluent and so reduces the overall quantumefiiciency of the overall device.

What is claimed is:

1. Phosphorescent composition represented by the formula Yb Er Ho M OClin which a is from 0.10 to 0.999175, b is from 0.000625 to 0.1, and c isfrom 0.0002 to 0.02, and in which M is at least one element selectedfrom the group consisting of yttrium, lutecium, gadolinium, lanthanumand scandium.

References Cited UNITED STATES PATENTS 3,541,018 11/1970 Hewes et a1.252-301.4 R 3,541,022 11/1970 Hewes 252301.4 S 3,591,516 7/1971 Rabatin252-301.4 R 3,607,770 9/1971 Rabatin 252--30l.4 R 3,666,676 5/1972Rabatin et a1. 252-301.4 R

OSCAR R. VERTIZ, Primary Examiner J. COOPER, Assistant Examiner t Column-5, line '49, M X

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTICN PATENT so.3,822,215

DATED July 2, 197A INVENTORs'S') William Grodkiewicz Shobha Singh, and

Grand G. Van Uitert ,Le o It Is CEItlflQd that error app-eats in theabove-adentmed patent and that said Letters Patent are hereby correctedasshown below:

10 3 1O Column 5, betweenlines 63-65, "Dg P nmm" should read --D Z -Pl/nmm--.

Column 5, line 72, after "typical" insert a period.

a n ,Column 7, lino 55, v Y )Yo Er OCl should read 7 ---(Y Yb Er OClColumn 8, line 16, "331/3" should read 33l/3%.

t '1 fl Column 9, line 29, CLOOl should read Cl I my 1 n Column 9, line19, I YO O7 should read Y H 3.8 Column 10, lines lO- ll, delete thesentence "Typical Column 10, line 1 4, should read -F indexapproximately that of the GaAs is preferred."

Signed and Sealed this AIIeSI.

RUTH C, MASON Arresting Officer C. MARSHALL DANN ('mnmisxinm'ruj'larcnls and Trademarks should read -M1+M 3+X

